This is my week for looking foolish. Wasn't looking in the right place. The ruling is covered in 37CFR part 201.40. Specifically:

37CFR 201.40.B.3
Computer programs and video games distributed in formats that have become obsolete and which require the original media or hardware as a condition of access. A format shall be considered obsolete if the machine or system necessary to render perceptible a work stored in that format is no longer manufactured or is no longer reasonably available in the commercial marketplace.

This appears to be what I was looking for. My apologies for wasting bitspace.

I promise that I have read the FAQ and tried to use the Search to answer my question.